During upgrade of vCenter Server from 7.0.3 to 8.0.3, there are now vSphere Distributed Switch MTU supported status errors on a few clusters.

Products

• VMware vCenter Server

Issue/Introduction

When Network Health Check is enabled on a vSphere Distributed Switch (vDS), you may observe the following behavior:

• Alarms are generated with messages about your VLAN and MTU configuration
  For example, "vSphere Distributed Switch MTU supported status"
• The monitor page for the vDS Health Check reports that some VLANs are Supported and some are Not Supported for the Physical Network Adapter under either VLAN and MTU.
• VLAN 0 shows as Not Supported

The load balancing policy on your vDS may be set to Route Based on IP Hash.

Environment

VMware vCenter Server 
VMware vSphere ESXi 

Cause

These alerts can trigger for a variety of reasons:

• A vDS is connected to multiple uplinks with different VLANs permitted.
  
  If the teaming/failover order is set on individual port groups to control which uplinks are used and each port group has been limited to using VMNICs where that VLAN is permitted, this will result in a working network configuration. However, Health Check does not distinguish between uplinks and will test each VLAN that is enabled for a VDS on each uplink. It will subsequently report a VLAN configured on the vDS as not supported for an uplink if it is not enabled on that particular network adapter. This affects the MTU, VLAN and Teaming & Failover test results.
  
  
• The MTU configured for your vDS exceeds the MTU set on a switch or router upstream of your host.
  
  The health check feature tests roundtrip connectivity which may transit multiple network devices. An MTU mismatch along the path can be detected even if the switch directly connected to your host has the correct MTU.
  
  
• The same alarm can also occur if a port group is configured with the VLAN type set to None. In this case, VLAN 0 shows as not supported.
  
  
• These alarms can trigger due to a combination of the Health Check protocol design and the Route Based on IP hash load balancing algorithm. If the load balancing policy for the vDS switch port is configured as Route based on IP hash and EtherChannel is configured in the connected physical switch, the physical switch may send the unicast frame to another uplink of the host where the broadcast was not sent as a result of the load balancing algorithm. This is not a bug or a design flaw in the health check protocol, load balancing algorithm or switch, but reflects the intended behavior of EtherChannel.
  
  
• You may receive alerts after restoring a distributed switch configuration, where the uplinks created initially are included in the vDS restore referencing previously allocated VLAN trunks that may no longer be in use.
  
  If this is the case, the original vDS uplinks can be removed: 
  
  

Resolution

This is the expected behavior with the Health Check feature in vSphere. The alarms inform you about configuration issues that you should be aware of.

Please refer below KB for the resolution and limitations of Network Health Check:
vDS Health Check reports unsupported VLANs for MTU and VLAN